The present invention relates to a valve timing control apparatus preferably used for optimizing an open or close timing of at least one of an intake or exhaust valve of an internal combustion engine in accordance with engine operating conditions.
Various valve timing control apparatuses are conventionally known as an advanced mechanism installed in an internal combustion engine for adjusting a rotational phase difference between a crank shaft and a cam shaft. For example, Published Japanese Patent Application No. Kokai 9-32519 discloses one conventional valve timing control apparatus for varying a valve timing and/or a lift amount of at least one of intake and exhaust valves by shifting a cam shaft in an axial direction to select a preferable cam engaged with the valve from different cams aligned in the axial direction. According to the conventional valve timing control apparatus disclosed in Published Japanese Patent Application No. Kokai 9-32519, a sleeve is interposed between a timing pulley and a cam shaft. This sleeve rotates together with the timing pulley and engages with the cam shaft through a spline engagement. With a controlled rotational phase difference, the driving force is transmitted from the crank shaft to the cam shaft. The cam shaft can cause a reciprocative slide movement in an axial direction.
To satisfy various requirements for improving engine performances, there is a necessity of more accurately controlling the valve timing of each intake or exhaust valve. However, a highly accurate valve timing control cannot be realized without improvement of the mechanical or hardware arrangement for controlling the rotational phase difference between the crank shaft and the cam shaft as well as improvement of an axial shift mechanism of the cam shaft equipped with a plurality of different cams.
Furthermore, according to the valve timing control apparatus disclosed in Published Japanese Patent Application No. Kokai 9-32519, a significant backlash is caused between splines (i.e., spline keys) in the spline engagement between the cam shaft and the sleeve. This backlash causes undesirable hammering noise from the spline engagement in response to a positive or negative variation of the torque applied on the cam shaft during the open and close control of the intake or exhaust valve.